Corneal trephines have been used in lamellar and penetrating keratoplasty. Originally, such trephines have been in the form of a honed cylinder as developed by Castroviejo. Many surgeons have attempted to improve the techniques as developed by Castroviejo, see U.S. Pat. No. 4,423,728. Many surgical companies have attempted to make holders for such cylinders in order to improve the visualization of the cutting edge but such attempts have generally been insufficient due to lack of proper centering, obscuration of the cutting edge at sometime during the procedure, independent eye and trephine movements, and lack of ability to cut other than round windows in the corneal tissue.
An improved corneal trephine was developed by David M. Lieberman, M.D., as described in the American Journal of Ophthalmology, May, 1976, pages 684-685. As described therein, the surgical instrument was comprised of inner and outer cones, the inner cone revolving within the outer cone. The outer cone included an upper ridge held by the non-dominant hand of the surgeon, stabilizing the instrument on the eye, and a lower ridge containing an annular suction device which firmly held the eye with a pressure of from 10-15 mm Hg to assure centration of the device over the cornea. The inner cone revolved within the outer cone and carried a slide mechanism with an attached disposable razor blade. To perform the incision, the inner cone which carried the blade was rotated about the cornea. After each rotation, the blade was lowered a few thousandths of an inch by turning a screw and the inner cone was rotated again. The incision could be viewed through an operating microscope. The slide mechanism upon which the blade was mounted was controlled by an adjustment screw for varying the radial position of the blade. Two interchangeable cutters could be used, one at a time. The first provided the razor blade at a 20.degree. angle. The second cutter mechanism held the blade vertically and was suitable for keratoplasty in which a donor cornea had been punched for reinsertion onto a patient's cornea.
Although the single trephine described above represented a significant advance in the art, the device could only provide a round cut and, consequently, could not be employed whenever an other than round incision was required.
A second improved corneal trephine was developed by David M. Lieberman, M.D., and is disclosed and claimed in U.S. Pat. No. 4,423,728 which disclosure is hereby incorporated herein by reference. The advantages of this trephine include the use of a circular or non-circular cam which guides the path of the cutting blade to provide either a circular or other than round cut of the cornea. As described therein, the surgical trephine comprises a base, a non-circular cam guide operatively connected to the base, and a rotation cone adapted to be disposed and rotated on the base, the rotation cone having a blade mounting means provided thereon. The blade mounting means includes a slide mechanism with an attached disposable razor blade and is further provided with a slave wheel which rides on the non-circular cam guide such that upon rotation of the circular rotation cone the blade means provides a cut of the cornea following the pattern of the annular cam guide. The razor blade is connected to the blade mounting means through a vertical adjustment screw such that upon adjustment of the screw, the blade could be moved vertically to control the depth of cut of the blade into the corneal tissue.
The above device was also provided with an angled blade mounting means which operated similarly to the vertical blade means to provide a cut within the corneal tissue in an other than vertical manner.
And, while the cam-guided trephine device described above and in U.S. Pat. No. 4,423,728 represented a significant advance in the art over the single point trephine described in the David M. Lieberman article, the cam guided trephine could still be improved. Specifically, the razor blade had a tendency to wobble during rotation of the blade, and the depth of cut of the cornea was difficult to accurately control. Further, since the complete cutting action of the corneal tissue was interrupted after each rotation of the blade means to incrementally lower the cutting blades, the cornea lamella is allowed to spread providing an uneven incision or "hour-glass" effect. Further, the process of making a complete cut through the corneal tissue was very slow. And, further, the sudden incremental lowering of the cutting blade for each new rotation of the blade means tended to displace the corneal tissue and thereby producing an uneven cut.